Electric fuse



April 29, 1941. BRANNQN 2,240,239

- ELECTRIC Fusi:

Filed Oct 10. 1958 ATTORNEY.

Psientedh r. 29.1941

" UNITED. STATES PATENT OFFICE Herbert E. Brannon, Detroit, Mich.

Application October 10, 1938, Serial No. 234,190 12 Claims. (01. zoo-113 .Due to the many electrical appliances that may be employed in residences, it often happens that the'lighting circuit is operated at substantially the capacity of the fuse. If the load on the line is substantially at the capacity of the fuse and an additional load, such as a motor of relatively high horse power is started, the line will be overloaded temporarily because of the large quantity of current required for starting the motor. This overload is not sufflcient to be dangerous. and is but temporary, but nevertheless the'fuse will burn out, thereby necessitating its replacement with a new fuse.

This invention aims to overcome the aforementioned disadvantages by providing -'a fuse which will not burn out except upon the occur rence of an unusually large overload caused by a short circuit or the like. It is an object of the invention, therefore, to provide a novel plug type fuse so constructed as to reduce the necessity for frequent fuse replacement.' It is another object of the invention to provide a plug type fuse which will break the electric circuit in which it is placed upon th mccurrence of a momentary overload on the line, but which will burn out only when an unusually large overload,- such as a short circuit, occurs. Still another object is to provide a simple fuse of the plug type which may be economically and readily manufactured, and which will invariably function properly.

In general, the invention. consists of a hollow cal in cross section.

shell which is adapted to be screwed into the usual fuse socket. Within the shell is a bimetallic resistor in series with a fusible metal link, and so arranged that current flowing in the line must-pass through the resistor and the fusible link. The resistor is supported in the shell so as to normally touch a contact point located in the shell, but is so arranged that upon a momentary overload of predetermined amount the resistor will become heated and bend or deflect away from the contact in the wall of the shell, thereby breaking the circuit. The fusible link is so constructed that it will carry a current slightly in excess of'that required to deflect the resistor but will melt if a suiilciently great overload occurs.

Inthe drawing: Figure 1 lsa cross-sectional view of a completed fuse, taken on substantially the line l-l of F g Figure 2 is a view taken on substal- .ally the line 22 of Figure 1 and looking in the direction of .the arrows; Figure 3 is a plan view of the fusible link before it is bent and assembled within the shell;

Figure 4 is a plan view of the resistor element;

Figure 5 is a cross-sectional, view taken on substantially the line 55 of Figure 4;

Figure 6 is a plan view of the electrical con- V tact ring;

Figure 7 is a cross-sectional view of the base of the shell taken onsubstantially the line "I-l of Figure 8;

Figure 8 is a plan view of the base;

'Figure 9 is a cross-sectional view of the me.-

tallic retaining ring; and

Figure'lo is a cross-sectional view similar to Figure 1 but showing the parts slightly separated from each other and in the order in which they are-placed when assembled.

The invention comprises an outer shell ll consisting of a body II and a base H. The two parts of the shell are preferably molded from a suitable insulating material, such as porcelain or a synthetic resin. The body II is hollow, as shown in Figures 1 and 10, and is substantially cylindri- The side wall of the body is provided with molded threads I3 for a purpose which will presently be described. At one end of the body is a notch It. The body is also provided with an annular groove l5 of somewhat larger diameter than the hollow in the body I I.

The base; l2, shown in Figures 1, 7, 8 and 10, is circular in plan and of a cross-section shown in Figures 1, '7 and 10. At one side of th base is a projection I6 which flts into and cooperates with the recess 14 in the body of 'the shell as shown in Figure 1, to properly locate the two parts and prevent their relative rotation. Adjacent the periphery of the base and on the surface juxtaposed to the body, the bas is provided with four slight protuberances H, the purposeof which will appear presently. The opposite surface of the base has four small recesses IS. The 1 center of thebase is apertured at l8 and in this aperture a rivet 20 is permanently secured. The rivet may be of any suitable conductive material. The rivet is upset at its outer end to form an The inner end of the rivet 2|"is capped at 22 with some material, such as silver, which resists oxidation from electricarcs.

A fusible link 23 having a free end 230 is secured at one end to a metallic ring 25. The ring is of substantially the same outer diameter as the groove 15 in the 'body ll of the shell ll.

Preferably the fusible link 24 and the ring 26 are made of the same material, such as zinc, and ar stamped from one piece of metal. The link 23 is cut out to form narrow necks 24. The cross section of these necks is such that the resistance thereof creates sumcient heat to melt them if a current flowing therethrough rises above a predetermined amount.

Figures 4 and 5 show the bimetallic resistor 26. The resistor is of cruciform shape having four arms 26a radiating from the center, as shown in Figure 4, and is made of thin sheets of two dissimilar metals 2! and 26 having their faces intimately secured together (see Figure 5). Soldered or otherwise to the center of the resistor 26 is a contact 29 of silver or other suitable material similar to the contact 22 on the base.

Figure 6 shows a conducting ring 30 of any suitable material, such as copper or brass.

Figure 10 shows the various parts spaced slightly apart and located in the order of assembly. The fusible link shown in Figure 3 is bent along the dotted line 3| into the shape shown in Figures 1 and 10, and assembled in the body of the housing as shown. The ring 25 rests at the bottom of the annular groove l6 and the free end 23a of the link 23 passes out through notch i4 and lies against the wall of body H. The resistor 26 is next placed in contact with the ring 25 of the fusible link with the arms 26a thereof in contact with the ring and the contact 29 facing toward the base l2 of the shell. The ring III is positioned over the resistor 26 and the base I2 is then located over the ring 30 and in contact with the body II. The protuberances ll on the base l2 touch the metallic ring 30 at four points intermediate the arms 26a of the resistor 26 so that the pressure directly on the arms of the resistor 26 will be light. It will be readily seen, therefore, that as all the pressure on the ring Ill comes at'points intermediate the arms 26a of the resistor, the arms may move slightly relative to the rings 25 and 36 to allow the resistor to deflect. The projection l6 on the base is located within the notch H in the side wall of the body II to prevent relative rotation of the base and body.

Over this entire structure the retaining ring 32 shown in Figure 9 is placed. This retaining ring is corrugated to form helical threads 33 and has a radially extending flange 34 at one end. The retaining ring is simply screwed on to the molded threads IS on the body to clamp the base against the body, and then the flange 34 is indented slightly to form projections 35 which extend into the recesses l6 in the base. The ring 32 touches the free end 23a of the fusible link 23 but is insulated from all other metal parts of the fuse.

The completed fuse is screwed into a fuse plug socket in the same manner as a conventional fuse plug. The retaining ring 32 forms one contact and the end 2| of the rivet 20 forms another contact which touch complementary contacts in the fuse plug socket. Normally the electric circuit is completed through the retaining ring 32, fusible link 24, resistor 26 and rivet 20. If the circuit in which the fuse is placed becomes temporarily slightly overloaded, the internal resistance of the resistor will cause it to heat, anddue to its bimetallic construction it will deflect away from the contact 23 and break the circuit- The resistor will then cool nently breaking the circuit and requiring the insertion of a new fuse. Such an overload is not likely to occur except due to a short circuit in the line which must be repaired before operation can be resumed.

The four arms 26a of the resistor 26 are short circuited by the rings 25 and 30 so that current must flow through all of the arms simultaneously to and from the contact 29 at the center of the resistor. The internal resistance and consequent heating capacity of the resistor is, therefore, .dependent on the cross section of these arms. By changing the cross section of the arms, or by varying their width or thickness, the quantity of current necessary to deflect the resistor may be changed, and fuses of different capacities made.

Another way of varying the capacity of the fuse is to place the resistor under an initial deflection when it is mounted within the shell I 0. This can be done by so locating the contacts 22 and 28 that the resistor is bowed slightly when the fuse is assembled. This arrangement is such that more heat and consequently more current is required to break the circuit, because the initial deflection must be overcome before the contacts 22 and 29 can move apart.

The fusible link should have a current capacity in excess of that required to actuate the resistor. This excess maybe of any reasonable amount, but 5 amperes has been found to give good results. Thus, if the resistor is designed to break the circuit if more than 15 amperes flows in the line, the fusible link should melt at 20 amperes. The design of a fusible link for a given capacity is well known so that it need not be discussed here.

It will be readily seen from the foregoing that this invention eliminates the necessity for replacement of fuses burned out by slight overloads, yet it gives unfailing protection against short circuits. The device is simple and readily assembled and may be substituted without change for a conventional fuse having only a fusible link therein.

It will be obvious that the structure herein disclosed is but one possible construction, and that the invention is capable of modification. Consequently, the invention is to be limited only by the scope of the appended claims.

I claim:

1. A plug type fuse including a shell having a hollow body and a base, a metallic contact in a wall of said shell and having portions located interiorly and exteriorly thereof, a bimetallic resistor of cruciform shape supported on the free ends of the arms thereof within the shell and having a portion thereof normally touching said contact and forming therewith an electrical conductor, a metallic ring engaging all of the arms of said resistor adjacent the ends thereof, a

and return to its initial position. As long as the second metallic contact in the wall of said shell, an electrical connection between said metallic ring and said second contact, said fuse being adapted to be connected in an electrical circuit, said resistor having the inherent capacity to deiiect itself away from said first contact and thereby break the electrical circuit in which it is lothe resistor.-

form shape supported by its arms within the shell and having a portion thereof adjacent the center of said resistor engaging said contact and forming therewith an electrical conductor, a metallic ring overlying the ends of the arms of the resistor and being in engagement therewith, a. plurality of protuberances on the inner face of the base engaging said metallic ring at points intermediate the arms of the resistor, a second metallic contact in a wall of said shell, an electrical connection between said metallic ring and said second contact, said fuse being adapted to be connected in an electrical circuit, said resistor having the inherent capacity to deflect itself away from said contact and thereby break the electric circuit in which it is located when the current flowing therein exceeds a predetermined quantity.

4. The combination recited in claim 3 wherein the electrical connection between the metallic ring and the second contact includes a fusible link having a current capacity slightly in excess of the quantity of current necessary to deflect the resistor.

5. The combination recited in claim 1 wherein the electrical connection between the metallic ring and the second contact includes a fusible link having a current capacity slightly in excess of. the quantity of current necessary to deflect 6. A circuit breaker comprising a shell,- two spaced contacts supported by a wall of said shell, a laminated metal resistor comprising a central portion and a plurality of arms extending radially outwardly therefrom, said resistor being mounted within the shell and supported thereon solely by the extremities of said arms for limited movement of the latter in the plane of the resistor, the central portion of the resistor being adapted to engage one of said contacts, and means connecting the extremities of the arms of the resistor to the other contact.

7. A circuit" breaker as defined .in claim 6 wherein said means includes a fusible link.

8. A circuit breaker as defined in claim 6 wherein the resistor is oi. cruciform shape.

9. A circuit breaker as defined inclaim 6 v wherein the shell comprises a hollow body and a removable base, and the extremities of the arms of the resistor are'positioned between the body and the base.

10. A circuit breaker as defined in claim 6 wherein the inner wall of the shell is recessed to loosely receive the extremities of the arms of the resistor. E

11. A circuit breaker comprising a shell including a hollow cylindrical body having an open end, a base closing said open end, a contact sup-' ported on said base, a retaining ring surrounding a part of said body and holding said body and base in associated relation, a laminated metal resistor comprising a central portion and a plurality of arms extending. radially outwardly therefrom, the extremities of said arms being loosely supported between said hollow body and base for limited movement of the former inthe plane thereof relative to the shell, the central portiou'of said resistorbeing adapted to touch said contact, and means connecting the extremities of the arms to said retaining ring.

12. A circuit. breaker as defined in claim 11 wherein said means includes a fusible link.

mam E. BRANNON. 

